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Heathkit W4-AM modifications

I am looking to refresh a pair of W4's. I have already purchased the 0.22uf caps and came across this thread with the modifications to make the amp stable. Can I still use the stock 0.22uf values or do I have to change the caps to 1uf and 0.15uf?
 
Zed -- The new coupling cap values on either side of the driver stage are absolutely key to achieving good LF stability in the W4. It really is important then to use the specified values.

Dave
 
dcgillespie said:
Zed -- The new coupling cap values on either side of the driver stage are absolutely key to achieving good LF stability in the W4. It really is important then to use the specified values.

Dave
Click to expand...

Thanks for the quick response Dave. For the pf values are Teflon caps warranted or just a decent poly?
 
I'm looking for an easy route to bypassing the pre-amp and provide power direct to the amplifier through s fuse and switch. Has any one tried and how did you do it?

Francis
 
Thanks!!

I have a very nice pair. Nicely refreshed by a prior owner, but no Dave's mods. Figured I really need to mod it (reduce b+, stability) and I have K-horns so lots of watts aren't needed, so will probably head down the Class A Triode path at the same time.
 
bigbargain said:
Thanks!!

I have a very nice pair. Nicely refreshed by a prior owner, but no Dave's mods. Figured I really need to mod it (reduce b+, stability) and I have K-horns so lots of watts aren't needed, so will probably head down the Class A Triode path at the same time.
Click to expand...

I love mine!
 
Probably a stupid question answered already, but what part number shows on the Chicago OPTs? I have two of these to rebuild, and none of the iron says "Chicago" anywhere on it, as I've seen in other photos. I have seen though, a photo of a W4-AM where the power transformer and choke were stamped "Chicago", but not the OPT, hence my question...
 
The Heath transformers don't say Chicago anywhere that I'm aware of. The actual Chicago equivalent best I can determine is the BO-13. I have a Williamson that was built with a BO-13 and it performs exactly the same, and the modifications to fix it also work exactly as expected. There is a small physical difference between the Heath iron and the Chicago iron though. The Heath is a flange mount with wire leads, the Chicago has 4 studs sticking out the bottom and you get a row of terminals on the bottom that have to be connected.
 
Do they actually have those? For some reason I'm thinking the W4 iron just has an internal Heathkit part number on it but I might be wrong on that. Pretty certain the W4 chokes I have list no other number besides the Heathkit one.
 
My EA-2's and several W5 type chokes all have EIA numbers. Maybe not all Heath items have them. I found one picture of a W4 and the EIA was printed with the Heath number.
 
Sometimes the numbers are on the mounting flange, and sometimes they are on the underside of the transformer as well.

Dave
 
I've had this same question for some time. I have four W4 output transformers and only one has a part # aside from 51-17. I can't see any way to distinguish between a Stancor and a Chicago.
 
maybe run some square waves and see if they actually perform differently. That would be the real question. If the performance is identical, I'd say it doesn't matter who actually made them.

Never really been clear on the Chicago / Stancor thing anyway. I was under the impression that the full name of that company was Chicago Standard Transfomer Company, and they shortened it to Stancor but I don't know if that was the result of a merger or if they were just running two brand names out of the same factory.
 
zackthedog said:
I've had this same question for some time. I have four W4 output transformers and only one has a part # aside from 51-17. I can't see any way to distinguish between a Stancor and a Chicago.
Click to expand...

You think there could be any small winding resistance differences that could be a tell? Or maybe inductance? Stancor and Chicago were related weren't they? Maybe there is no difference.
 
OK, first transformer:
51-17 (Heath part #)
138639, which would be Stancor make

2nd transformer:
51-17
138759, also Stancor
Thanks for the tips on the EIA codes, I had forgotten that those things existed!

Both are flange-mount, cloth-covered wires out the bottom. I'll build them without the imbalance modification in place, then test. If they need it, it's trivial to add one 220K resistor
Thanks all!
 
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